Originally Posted by Katsunami
Many such services have statements in their EULA that say something akin to this:
"When The Provider suspects that you are using The Service to host copyrighted material for which you do not have distribution rights, The Provider is allowed to close down your account without further notice."
In short, if you put a lot of books into DropBox and they come to the conclusion that "2000 books have to be illegal stuff, nobody reads that much", then you could lose everything at once. They might even notify authorities to check it out.
Not trying to scare you out or anything, but I'd NOT put huge amounts of books into a storage locker such as DropBox.
People have been using Dropbox for ebooks for a long time. Unless you are sharing links no one would know what's in your DB. Dropbox does not go looking into your files. They have said this time and time again. Just keep your stuff out of the public folder and you will be fine.